The present invention relates to a device for positioning components with high precision. In particular, the present invention relates to a parallel kinematic manipulator capable of positioning components with nanometer tolerances.
The precise positioning of components is increasingly important. For instance, optical communications systems require that the ends of optical fibers be precisely aligned with mating components or fibers to ensure minimal transmission losses. The precision alignment of components is also important in connection with the manufacture of semiconductor devices, and with devices having miniaturized components and/or fine tolerance requirements. As yet another example, precision surgery applications, including remote surgery, require the ability to precisely control the position and movement of instruments. However, previous attempts at providing for the precise positioning of a component or instrument have been incapable of providing high resolution positioning. In particular, previous attempts at providing devices capable of precisely positioning components and instruments have been incapable of providing a desired number of degrees of freedom in combination with a desired positioning tolerance.
Manipulators or positioners capable of providing a number of degrees of freedom are available. One such type of device is a manipulator having stacked stages. An example of a manipulator 100 incorporating stacked stages is illustrated in FIG. 1. The manipulator 100 includes first 104, second 108 and third 112 linear stages for providing linear movement of the mobile plate or tool plate 116 relative to the base plate 120. In particular, the linear stages 104, 108 and 112 provide movement of the mobile plate 116 with respect to the base plate 120 along the x, y and z axes. In addition, a first 124 and second 128 rotational stage are provided to rotate the mobile plate 116 with respect to two separate axes. The combination of three linear stages 104, 108 and 112 and two rotational stages 124 and 128 provides a manipulator 100 having five degrees of freedom.
Although the manipulator 100 is capable of providing five different movements for positioning a component or instrument interconnected to the mobile plate 116, the resolution or step size with which such positioning can be accomplished is limited. In particular, manipulators having stacked stages, such as the manipulator 100 illustrated in FIG. 1, suffer from additive positioning errors. Specifically, there are sine and cosine position errors associated with each movement, in addition to linear (or rotational) position errors. Errors associated with each stage can contribute additively to an overall positioning error associated with the manipulator. As a result, even if great efforts are made to accurately control the position of each stage, the overall positioning error remains relatively high. For example, if each linear actuator has an error of 50 nm, the overall positioning error of the manipulator is likely to be at least 150 nm. Adding in errors associated with the rotational stages, and sine and cosine errors, a high quality, 5 degree of freedom manipulator 100 having stacked stages is likely to have 250 nm or more of position error.
Parallel mechanisms provide a manipulator structure that avoids additive errors. In a parallel mechanism, such as the parallel mechanism 200 illustrated in FIG. 2, a base plate 204 is interconnected to a mobile plate 208 by a plurality of kinematic links 212. In the parallel mechanism 200 illustrated in FIG. 2, six kinematic links 212a-f are provided. As a result, the parallel mechanism manipulator 200, also known as a hexapod, is capable of moving the mobile plate (tool plate) 208 with six degrees of freedom (x, y, z, "PHgr", xcex8, "psgr"). Because the position error of a parallel mechanism is not additive, higher positioning tolerances are possible than with a stacked stage type device (e.g., manipulator 100 in FIG. 1). For example, if positioning resolutions of 50 nm are available with respect to each kinematic link, a parallel mechanism type manipulator such as the manipulator 200 illustrated in FIG. 2 might be capable of positioning the mobile plate 208 with a resolution that is also about equal to 50 nm. Although such resolution is acceptable in many cases, it is still too high for may applications, particularly aligning fiber optic cables. At the same time, it is also desirable to provide actuators capable of operating at high velocities, for example, to speed up production processes. Typical actuators include servo motors, linear motors and inch worm type ceramic actuators.
Servo motor type actuators may suffer from backlash associated with the screw-type jacking mechanisms often used to effect changes in the length of the kinematic link. In addition, servo and linear motor type actuators suffer from dithering, which involves high frequency, small amplitude movements of the motor as it searches for the correct position. Such dithering can result in vibrations that can interfere with intended positioning operations, even when changes in the lengths of the kinematic links are not being effected.
Inch worm-type piezoelectric motors generally include a pair of ceramic rings capable of selectively engaging a rod running through the rings. In particular, the ceramic rings can be electrically excited in such a way as to controllable move the rod with respect to the rings. Although such devices are capable of providing small changes in the length of a kinematic chain, they suffer from inaccuracies due to hysteresis. Therefore, it is difficult to accurately control the length of a kinematic chain utilizing an inch worm-type piezoelectric actuator. The operation of such devices is also relatively slow. In addition, the operation of inch worm-type piezoelectric actuators creates vibrations that can interfere with the intended positioning operations.
Therefore, there is a need for a method and apparatus capable of providing for the precise positioning of a component or instrument. In particular, there is a need for a method and apparatus for providing a manipulator capable of positioning a component or instrument with high repeatability, resolution, and speed, without dither.
In accordance with the present invention, a parallel kinematic micromanipulator is disclosed. Also disclosed is a method for precisely positioning a component or instrument. The method and apparatus of the present invention allows for the positioning of components and instruments with extremely high repeatability and allows multiple degrees of freedom in the movement of a component or instrument.
The inventor of the present invention has recognized that higher positioning resolutions than are available using prior art manipulators would require kinematic links capable of having their lengths controlled with greater precision. Furthermore, the inventor of the present invention has recognized that the inaccuracies encountered with respect to the position of individual kinematic links are in large part due to the inaccuracies inherent to the actuators used to control the length of the kinematic links. Such actuators have included servo motors, linear motors, and inch worm-type ceramic actuators. In contrast, the present invention comprises linear piezoelectric actuator assemblies capable of providing movement with resolutions that have not been available in connection with conventional manipulators. As can be appreciated by one of skill in the art, piezoelectric actuators take advantage of the piezoelectric effect exhibited by certain crystals, in which the application of an electric field causes the crystal to expand or contract in certain directions. Furthermore, the linear piezoelectric actuator assemblies utilized in connection with the present invention are capable of providing motion that is substantially continuous, as opposed to the intermittent, start-stop type motion provided by inch worm type piezoelectric devices.
In accordance with an embodiment of the present invention, a parallel mechanism comprising at least three kinematic links is provided. Each kinematic link comprises at least a first piezoelectric linear actuator capable of providing repeatable movement of its respective link with a resolution of no more than about 10 nm. Such a micromanipulator is capable of positioning components or devices with very high repeatability and resolution and can provide at least three degrees of freedom.
According to another embodiment of the present invention, a micromanipulator comprising a hexapod type parallel mechanism is provided. Furthermore, each of the six kinematic links of the hexapod comprises a piezoelectric linear actuator assembly. The combination of the parallel mechanism configuration with piezoelectric actuators results in a micromanipulator capable of providing movements having resolutions of 10 nm or less. In addition, such an embodiment of the present invention is capable of providing a micromanipulator having six degrees of freedom.
According to a further embodiment of the present invention, parallel mechanisms are provided comprising a plurality of kinematic links. Each kinematic link comprises a piezoelectric linear actuator assembly comprising at least two piezoelectric ceramic elements. According to still another embodiment of the present invention, the piezoelectric linear actuator assemblies each comprise at least a first rectangular piezoelectric ceramic element interconnected to a carrier member and having a plurality of electrodes that can be excited to produce controlled movement of a slide member. According to yet another embodiment of the present invention, the piezoelectric linear actuator assemblies comprise dual mode standing wave motors.
In accordance with another embodiment of the present invention, a method for precisely positioning components or instruments is provided. According to the method, a mobile plate is interconnected to a base plate by a plurality of kinematic links. Each of the kinematic links comprises at least a first piezoelectric linear actuator assembly. A first component or instrument is interconnected to the mobile plate, while a second component, assemblage or body is placed in a fixed position relative to the base plate. Electrical excitation is selectively provided to a plurality of the piezoelectric linear actuator assemblies to effect movement of the mobile plate with respect to the base plate. In particular, electrical excitation is selectively provided to the piezoelectric linear actuator assemblies to move the component or instrument interconnected to the mobile platform in any of a plurality of directions. In accordance with an embodiment of the present invention, movement may be provided along any one of three axes. According to still another embodiment of the present invention, translational movement may be provided with respect to three axes, and rotational movement may be provided about any of the three axes.
Based on the foregoing summary, a number of salient features of the present invention are readily discerned. A micromanipulator capable of controlled movement in a variety of directions is provided. The amount of movement may be controlled with a high degree of precision and repeatability. The present invention is well-suited for applications requiring the alignment of precision componentry, such as in connection with the alignment of optical fibers. In addition, the present invention is well suited to applications requiring precisely controlled movements, such as surgical applications.